When developers first encounter CodePipeline, it looks like Jenkins wrapped in a web UI. If you start learning with that understanding, you'll hit a wall at exam questions. What DOP-C02 asks about pipelines is not "how to use it" but rather "why designed this way, what combination is correct for this scenario." To reach that answer, you must understand what problem the CodePipeline hierarchy was designed to solve.
When Jenkins launched in 2004 under the name Hudson, a pipeline was simply a chain of jobs. "When A finishes, start B." The problem emerges as organizations grow